The invention relates to a hydrostatic-mechanical drive unit for a mixing drum, especially of a mobile concrete mixer. The drive unit has a hydraulic pump connected to a hydraulic motor via lines. The hydraulic pump is surrounded by a housing. A transmission housing accommodates the hydraulic motor and a planetary transmission. A component of the planetary transmission is in driving connection with an input flange of the mixing drum.
A hydrostatic-mechanical drive unit of the configuration explained above has been disclosed in DE-A 43 13 025. To improve the cooling of the unit, oil is steadily fed from a high-pressure circuit to the drive unit. Also, cooled oil is steadily fed to the interior of the transmission housing in such a manner that cooling of the hydraulic motor also results. The hydraulic motor is preferably a slowly working radial-piston motor. The pistons of the radial-piston motor bear, via rollers, on a cam surface which has a course substantially shaped as a sine wave. Each piston is biased into the cylinder block under the action of a spring component. The spring components can be formed, for example, of compression springs. They produce a constant, positive connection between the rollers of the pistons and the cam surface. It is thus ensured that the piston spaces always remain filled with oil. This arrangement reduces the further oscillation of the concrete mixer drum when an internal combustion engine is shut down.
This invention is based on the problem of further improving the arrangement for preventing further oscillation of the mixing drum without too much extra construction cost.